This invention relates in general to the Roots type supercharger and, more specifically, to improvements in reliability and operation of Roots type superchargers.
Internal combustion engines have long used superchargers of one type or another to get more air into the engine to permit more fuel to be burned and increase engine power output. A variety of superchargers have been developed, including vane type, turbochargers and Roots type superchargers.
Roots type superchargers have come into widespread use with racing automobiles, motorcycles, boats and the like because of their high efficiency and reliability. In its simplest form, a Roots type supercharger consists of two elongated rotors, each shaped like a FIG. 8 in cross section, running between end plates in an oval-shaped housing, on parallel shafts and geared together so that the rotor lobes are always in line contact. Clearances between the rotors and between rotors and the housing and end plates are kept to a minimum but with no direct contact. As the rotors rotate they collect air from an inlet in the housing and carry it around the outside and direct it to an outlet at higher pressure. Linear seals of high temperature resistant materials, such as Teflon fluorocarbon resins, may be embedded in longitudinal grooves in the faces of the lobes to contact the opposite rotor when meshed therewith to reduce air leakage therethrough.
While present Roots type superchargers are efficient, I have found that one problem significantly adversely affects operation and useful lifetime. As one lobe begins to mesh with the adjacent rotor, particularly with the linear seal arrangement, a small amount of air is rapidly compressed between the lobe and opposite rotor. The air pressure tends to very slightly bend the rotor and to escape by forcing the end plates slightly away from the rotors. Repeated many millions of times, these forces gradually adversely affect operation of the supercharger by forcing the components out of alignment and shape. Also, compression heating of the air compressed at the nip between lobes can significantly increase the temperature of the rotors and charge air. In order to assure a long effective lifetime for the supercharger, I have found that these forces must be reduced or eliminated.
Thus, there is a continuing need for improvements in Roots type superchargers.